In general, a water pump is installed in a drain water tank of a washing machine, or is used for circulation of a coolant that cools an engine.
The water pump includes: a drive unit for generating a driving force under a power-on situation; and a pump unit that is connected to the drive unit which pumps water. Since the water pump performs functions of pumping the water, the water flowing into the drive unit results in a failure of the drive unit. Accordingly, a pump with a mechanical seal structure or a canned pump having a canned cover structure of sealing a stator is used for the purpose of protecting the drive unit from the water.
Since U.S. Pat. No. 4,277,115 that proposed a canned pump employs a structure in which a canned cover seals only a stator, a rotor is sunk in water, to thus adversely affect the durability of bearings supporting a rotating shaft. In addition, a magnetic gap cannot be optimally maintained due to a canned cover disposed between the rotor and the stator, to thus cause a problem of falling efficiency.
In addition, in the case of the canned pump, since the rotor is sunk into water, the rotation of the rotor is affected and the motor efficiency is lowered.